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Electrical Double Layer





HISTORICAL DEVELOPMENT OF DOUBLE LAYER MODELS

The earliest model of the electrical double layer is usually attributed to Helmholtz ( 1879 ). Helmholtz treated the double layer mathematically as a simple capacitor, based on a physical model in which a single layer of ions is adsorbed at the surface.

Later Gouy and Chapman ( 1910 - 1913 ) made significant improvements by introducing a diffuse model of the electrical double layer, in which the potential at a surface Decreases Exponentially due to adsorbed counter-ions from the solution.

The current classical electrical double layer is the Gouy-Chapman- Stern model, which combines the Helmholtz single adsorbed layer with the Gouy-Chapman diffuse layer. Important approximations used in this model are:
  • Ion s are effectively point charges

  • The only significant interactions are Coulomb ic

  • Electrical Permittivity is constant throughout the double layer

  • The solvent is uniform at the atomic scale.